DE 197 35 058 A1 discloses a cooling system for an internal combustion engine with a liquid coolant, a heat exchanger of an additional device being connected to the circuit for the coolant by means of a switching valve. The switching valve contains as a switching element a thermostatic operating element, which is arranged in a valve chamber. The valve chamber, which can be shut off with respect to the heat exchanger of the additional device by means of the valve element, is adjoined by a supply connection and a return connection for the coolant, so that, even when the connection to the heat exchanger of the additional device in the valve chamber is shut off, a coolant flow is still maintained. This is intended in particular to reduce the reaction time of the switching valve, since the flowing coolant has the effect in particular of helping to cool down a thermostatic operating element.
Thermostatic valves have already been known for some time and are used in particular for automatic temperature control. Expansion elements are usually used for this purpose in such thermostatic valves and may be formed for example as wax elements. To allow such a thermostatic valve to be actively operated, a heating resistor is usually additionally provided, and when an electric current is applied to this resistor it causes the wax element or the expansion element to heat up and thereby expand, which is accompanied by an opening or closing of the thermostatic valve. The heating resistor is in this case normally fitted with a corresponding contacting system in a thermostat housing part with an encapsulated contact assembly. However, the encapsulation of the contact assembly in the thermostat housing part requires a comparatively complex injection mould. In most cases, the encapsulation of the contacts even necessitates a preassembled unit, which further increases the effort involved in production. Furthermore, the dimensional tolerances of the expansion element receptacle have to meet demanding requirements, which require a great effort to be invested in the making of the mould.
The thermostat housing part has the task not only of receiving the electrical contacting but also of providing the element receptacle and of presenting the customized connector geometry. It must also be possible in addition for an impermeable shielding of the contacting system with respect to the coolant circuit to be produced. As a further important requirement, the plastic encapsulation of the electrical contacts must conform to corresponding types of protection for engine compartment conditions and protect the electrical contacting system from environmental influences, such as for example saltwater, high-pressure steam jets, deep stretches of water or the like. Impermeable encapsulation of the electrical contacting system in turn greatly restricts the choice of material in terms of the plastics that can be used for this, so that for example only high-grade, and consequently expensive, plastics can be used, and at the same time the entire thermostat housing part also has to be produced from this material even though it is actually only required in the region of the expansion element receptacle.
Other disadvantages that have been found with thermostatic valves known from the prior art are that establishing the electrical contacting often requires a complex subassembly, which consists of a plastic preform and other components and has to be produced in a number of joining processes. In most cases, two further encapsulations are required before a complete thermostat housing part or a complete thermostat cover has been completed in this way. Such multiple encapsulations always entail the risk however of air pockets and trouble spots where the polymer materials do not melt, both of which can lead to leakages under sustained extreme conditions. Since the expansion element in conventional thermostatic valves is often also not connected to the thermostat housing part with a form fit, under unfavourable flow conditions it can be displaced from its tight fit. Even profiled seals fitted to the expansion element for sealing a valve head from the thermostat housing part entail a disadvantage, because a different choice of guides is required since the seal can become detached from the sealing groove under unfavourable flow conditions. This happens in particular at the time of the opening or lifting off of the valve head from the seal, if great flow rates occur because of the small gaps. When the valve head has been raised to the extent that the outside diameter of the seal is just exposed and the seal is no longer pressed into the O-ring groove by the valve head, there is the risk of the sealing ring being washed completely out of the sealing groove. Similar conditions occur during the closing of the valve head.